Patent Application
20240342785
The present invention relates to a tubular rotary component made from a metal plate as a material, a method and a mold for manufacturing such a tubular rotary component. In particular, the present invention relates to a tubular rotary component that is made from a rolled steel plate as a material, and is for use as a bearing ring of a rolling bearing, a bearing ring for a roller, and a gear component.
Today, many of rotary components having a tubular shape, such as rolling bearings, rollers, and gear components, are made from seamless steel tubes that are produced from round bars of special steel (Patent Document 1).
Such a round bar of special steel as a material for the seamless steel tube contains inclusions, such as Al2O3, MnS, and TiN, that are unevenly distributed. The quantity of the inclusions increases toward the center and reaches a maximum at a central portion. The seamless steel tube is formed by piercing and reaming a central hole of the round bar by the Mannesmann piercing method. Therefore, the quantity of inclusions reaches a maximum near an inner peripheral portion of the steel tube, and decreases toward the outer periphery.
The inclusions may serve as a starting point of a fatigue fracture. It is known that if a large quantity of inclusions is present in or near a surface layer of a slidable component, fatigue characteristics of the slidable component (and rolling fatigue characteristics in the case of a rotary component) are deteriorated significantly (see Patent Document 2). Therefore, in the case of producing a tubular rotary component from a seamless steel tube as a material, to obtain desired fatigue characteristics, it is necessary to subject the tubular rotary component to machining. For example, the tubular rotary component needs to be cut in a direction from the inner periphery to the outer periphery to the extent that the inclusions exert a small effect. As a result, material yield decreases.
To address this problem, a method for manufacturing a tubular rotary component with satisfactorily material yield is disclosed. According to this method, a doughnut-shaped disc made of a steel plate as a material and having a hole in a central portion is subjected to a drawing process to be molded into a tubular rotary component (see Patent Documents 3 and 4).
A quantity of the above-mentioned inclusions increases toward the midpoint of a plate thickness of a steel plate and reaches a maximum near the midpoint of the plate thickness. Therefore, in the case of producing a tubular rotary component from a steel plate as a material, it is unnecessary to cut an inner peripheral portion of the tubular rotary component for the purpose of removing the inclusions, unlike the case of a tubular rotary component made from a seamless steel tube. As a result, it is possible to increase the material yield.
As illustrated in
To address this problem, it is possible to employ the method for manufacturing a tubular structure disclosed in Patent Document 4 (see
Therefore, it is an object of the present invention to provide a method and a mold for manufacturing a tubular rotary component from a doughnut-shaped metal disc while reducing occurrence of wrinkles and cracks due to a drawing process, and to provide such a tubular rotary component.
The present invention relates to a method for manufacturing a tubular rotary component from a metal disc with a hole formed in a central portion thereof, the metal disc having a predetermined inside diameter and a predetermined outside diameter. The method includes: an intermediate molding step including subjecting the metal disc to a reaming-drawing process in which both surfaces of the metal disc are pressed in entirety by a tapered surface of a punch having a predetermined taper and a tapered surface of a die having a predetermined taper, thereby producing an intermediate molded article having a frustoconical shape; and a final molding step including subjecting the intermediate molded article to a further reaming-drawing process in which the intermediate molded article is pressed by a punch and a die having a smaller taper angle than the punch and the die for use in the intermediate molding step, respectively, thereby manufacturing the tubular rotary component.
The processes are preferably performed under a condition that a stretch flange rate λ is 90% or less, the stretch flange rate λ being given by λ=(D1′−D1)/D1×100 where D1 represents the inside diameter of the metal disc before undergoing the processes, and D1′ represents an inside diameter of the tubular rotary component manufactured through the final molding step.
In the intermediate molding step, an angle formed between the tapered surface of the punch and a processing direction and an angle formed between the tapered surface of the die and the processing direction are preferably each set to 30 degrees or greater.
In the intermediate molding step, the reaming-drawing process is preferably performed two or more times while an angle between the tapered surface of the punch and a processing direction and an angle between the tapered surface of the die and the processing direction are varied.
The metal disc is preferably made of a metal plate as a material, the metal plate containing inclusions that are unevenly distributed such that a quantity of the inclusions increases toward a midpoint of a plate thickness of the metal plate. Preferably, the method further includes a cutting process step including subjecting the tubular rotary component obtained through the final molding step to a cutting process. The tubular rotary component has a thickness in which a partial thickness from a midpoint of the thickness to an inside diameter-side surface of the tubular rotary component is defined as an inside diameter-side thickness, while a partial thickness from the midpoint of the thickness to an outside diameter-side surface of the tubular rotary component is defined as an outside diameter-side thickness. The cutting process is preferably performed such that an inside diameter-side residue ratio becomes 0.37 or greater and an outside diameter-side residue ratio becomes 0.49 or greater, the inside diameter-side residue ratio being a ratio of the inside diameter-side thickness after the cutting process to the inside diameter-side thickness before the cutting process, and the outside diameter-side residue ratio being a ratio of the outside diameter-side thickness after the cutting process to the outside diameter-side thickness before the cutting process.
Preferably, the method further includes a heat treatment step including subjecting the tubular rotary component obtained through the final molding step to hardening and tempering.
The present invention further relates to a mold for use in the method described above. The mold includes: a punch with a predetermined taper and a die with a predetermined taper that are for use in the intermediate molding step; and a punch and a die that have a smaller taper angle than the punch and the die for use in the intermediate molding step, respectively.
The present invention relates to a tubular rotary component manufactured by the method described above. The tubular rotary component has a thickness in which a partial thickness from a midpoint of the thickness to an inside diameter-side surface of the tubular rotary component is defined as an inside diameter-side thickness, while a partial thickness from the midpoint of the thickness to an outside diameter-side surface of the tubular rotary component is defined as the outside diameter-side thickness. An inside diameter-side residue ratio is 0.37 or greater and an outside diameter-side residue ratio is 0.49 or greater, the inside diameter-side residue ratio being a ratio of the inside diameter-side thickness after the cutting process to the inside diameter-side thickness before the cutting process, and the outside diameter-side residue ratio being a ratio of the outside diameter-side thickness after the cutting process to the outside diameter-side thickness before the cutting process.
The present invention further relates to a tubular rotary component having a distribution of inclusions in a plate thickness of the tubular rotary component. When a quantity of the inclusions present in an inside diameter-side surface layer is defined as d (inside diameter) and a quantity of the inclusions present at a midpoint of the plate thickness is defined as d (plate thickness midpoint), the distribution satisfies a relationship expressed as d (plate thickness midpoint)>d (inside diameter).
The inclusions may contain at least one selected from the group consisting of MnS, SiO2, Al2O3, and TiN.
The manufacturing method of the present invention, which includes the intermediate molding step including subjecting the metal disc to a drawing process in which both surfaces of the metal disc are pressed in entirety by the tapered surface of the punch and the tapered surface of the die, makes it possible to reduce occurrence of wrinkles and cracks. The manufacturing method of the present invention can manufacture a tubular rotary component having a desired shape through the final molding step.
Preferred embodiments of a method and a device for manufacturing a tubular rotary component of the present invention will be described with reference to the drawings. The tubular rotary component of the present invention is for use as a bearing ring of a rolling bearing, a bearing ring for a roller, and a gear component, and is required to have superior rolling fatigue characteristics.
The shape of the metal disc 100 can be suitably determined by setting the inside diameter D1, the outside diameter D2, and the plate thickness H from a volume of a desired tubular rotary component 100B having a final shape. Examples of a material for the metal disc 100 include metal plates such as a rolled steel plate. A rolled steel plate contains inclusions that are unevenly distributed in such a manner that a quantity of the inclusions increases toward a midpoint of the plate thickness of the rolled steel plate. Therefore, superior rolling fatigue characteristics can be obtained by way of a drawing process performed on the rolled steel plate so that a surface of the rolled steel plate is formed into a load-bearing surface. In this way, sufficient rolling fatigue characteristics can be obtained without using a rolled steel plate having a high index of cleanliness.
As illustrated in
As illustrated in (a) in
The tapered surface of the punch 10A and that of the die 20A form an angle θp and an angle θd with a processing direction, respectively. In the present embodiment, the angles are set to satisfy the relationship expressed as θp=θd in order to make the produced tubular rotary component have a uniform thickness.
Setting the angle θp of the punch 10A and the angle θd of the die 20A to 25 degrees or greater makes it possible to produce the intermediate molded article 100A while reducing occurrence of cracks. Setting the angles θp and θd to 30 degrees or greater makes it possible to produce the intermediate molded article 100A while reducing occurrence of minute wrinkles.
As illustrated in (b) in
Note that the “intermediate molding step” as used herein refers to subjecting the metal disc or the intermediate molded article to the reaming-drawing process, while both surfaces of the metal disc or the intermediate molded article are pressed in their entirety by the tapered surfaces. The “final molding step” as used herein refers to a step in which the intermediate molded article is subjected to the reaming-drawing process while both surfaces of the intermediate molded article are pressed in their entirety, but not by tapered surfaces.
Next, a stretch flange rate λ in the process in which the metal disc 100 is molded into the tubular rotary component 100B will be described.
Based on the inside diameter D1 of the metal disc 100 before the reaming-drawing process and the inside diameter D1′ of the tubular rotary component produced through the final molding step, the stretch flange rate λ is given by λ(%)= (D1′−D1) D1×100. If the inside diameter D1′ resulting from the final molding step is excessively large with respect to the inside diameter D1 before the reaming-drawing process, the risk of cracks arises. Therefore, it is preferable to set the shape of the metal disc 100 such that the stretch flange rate λ will be 90% or less.
The above-described method for manufacturing the tubular rotary component according to the present embodiment produces the following effects.
(1) The method is for manufacturing the tubular rotary component 100B from the doughnut-shaped metal disc 100 having the predetermined inside diameter D1 and the predetermined outside diameter D2. The method includes: the intermediate molding step including subjecting the metal disc 100 to the reaming-drawing process in which both surfaces of the metal disc 100 are pressed in their entirety by the tapered surfaces of the punch 10A with the predetermined taper and the die 20A with the predetermined taper, thereby producing the intermediate molded article 100A having a frustoconical shape; and the final molding step including subjecting the intermediate molded article 100A to the further reaming-drawing process in which the intermediate molded article 100A is pressed by the punch 10B and the die 20B that have a desired shape, thereby producing the tubular rotary component 100B. This feature makes it possible to mold the metal disc 100 into the tubular rotary component 100B, while reducing occurrence of cracks and wrinkles during the reaming-drawing processes. In the case of using a steel plate as the material for the metal disc, the tubular rotary component 100B can be made to have sufficient rolling fatigue characteristics.
(2) According to the manufacturing method of the present invention, the processes are carried out under the conditions that the stretch flange rate A is 90% or less, the stretch flange rate λ being given by λ=(D1′−D1)/D1×100 where D1 represents the inside diameter of the metal disc 100 before undergoing the processes and D1′ represents the inside diameter of the tubular rotary component 100B produced through the final molding step. This feature makes it possible to produce the tubular rotary component 100B, while reducing occurrence of cracks.
(3) In the intermediate molding step, the angle θp formed between the tapered surface of the punch 10A and the processing direction and the angle θd formed between the tapered surface of the die 20A and the processing direction are each set to 30 degrees or greater. This feature makes it possible to produce the tubular rotary component 100B, while reducing occurrence of minute wrinkles.
Next, a modification of the present embodiment will be described with reference to
As illustrated in (a) in
A tapered surface of the punch 10A1 and that of the die 20A1 form an angle θp1 and an angle θd1 with a processing direction, respectively. In the present modification, the angles are set to satisfy a relationship expressed as θp1=θd1 in order to make the produced tubular rotary component have a uniform thickness.
As illustrated in (b) in
A tapered surface of the punch 10A2 and that of the die 20A2 form an angle θp2 and an angle θd2 with the processing direction, respectively. In the present modification, the angles are set to satisfy a relationship expressed as θp2=θd2 in order to make the produced tubular rotary component have a uniform thickness. The angles θp2 and θd2 formed between the processing direction and the tapered surfaces of the punch 10A2 and the die 20A2 for use in the second reaming-drawing process are smaller than the angles θp1 and θd1 formed between the processing direction and the tapered surfaces of the punch 10A1 and the die 20A1 for use in the first reaming-drawing process.
As illustrated in (c) in
The method for manufacturing the tubular rotary component according to the present modification produces the following effects.
(4) In the intermediate molding step, the reaming-drawing process is performed two or more times, while the angle between the tapered surface of the punch and the processing direction and the angle between the tapered surface of the die and the processing direction are varied. This feature makes it possible to carry out the intermediate molding step further suitably, in comparison with the case where the intermediate molding step includes performing the reaming-drawing process once.
Next, with reference to
A SUJ2 steel plate having a plate thickness of 6 mm was used as the material for each metal disc 100. The reaming-drawing process of the intermediate molding step and that of the final molding step were performed under the drawing process conditions shown in Table 1.
The tubular rotary components of the Examples and Comparative Examples were produced with different values of the stretch flange rate A. The tubular rotary components of Examples 1-1 to 1-3 were produced using the molds illustrated in
The tubular rotary components of Examples 1-1′ to 1-3′ and Examples 2-1′ to 2-3′ were produced using the molds illustrated in
For the purpose of comparison with the conventional manufacturing methods, the tubular rotary component of Comparative Example 2 was produced using the mold disclosed in Patent Document 1, as illustrated in
Table 2 shows the specifics of the shapes of the metal discs 100 used in Examples and Comparative Examples. Table 3 summarizes the results of the drawing process tests.
As shown in Table 3, a comparison between the stretch flange rates of Examples 1-1 to 2-3 and Comparative Example 1 demonstrates the following. Examples 1-1 to 2-3 of which the stretch flange rate A was 90% or less allowed the reaming-drawing processes to be performed, with the absence of cracks, as shown in
Regarding Examples 1-1′ to 1-3′ and Examples 2-1′ to 2-3′ in which the intermediate molding step is carried out once and is followed by the final molding step, it was confirmed that if the reaming-drawing process is performed in a state where the angles θp1 and θd1 of the tapered surfaces are 25 degrees or greater, the drawing process can be performed suitably although minute wrinkles are observed after the final molding step. It was also confirmed that if the reaming-drawing process is performed in a state where the angles θp1 and θd1 of the tapered surfaces are 40 degrees or greater, the reaming-drawing process can be performed without allowing minute wrinkles to form.
In Comparative Examples 2-1 and 2-2, the same metal discs 100 as those of Examples 2-1 to 2-3 were used. That is, under the same condition that the stretch flange rate A is 85%, the reaming-drawing process of the final molding step was performed using the conventional mold, while the intermediate molding step was omitted. Comparative Examples 2-1 and 2-2 experienced cracks, making it impossible to produce tubular rotary components.
Next, with reference to a case where a tubular rotary component produced through the reaming-drawing process is subjected to a cutting process, an effect exerted on the rolling fatigue characteristics by a cutting volume will be described.
With reference to
In the case of the metal disc made of steel, the inclusions generally contain three types of inclusion: namely, A type inclusions, which have undergone viscous deformation due to a process; B type inclusions, which form groups of particles arranged discontinuously in the processing direction; and C type inclusions, which have not undergone viscous deformation and are irregularly dispersed. Known representative non-metallic inclusions of A type inclusions include, for example, MnS as a sulfide having an elongated shape and SiO2 as silicate. Known representative non-metallic inclusions of B type inclusions include, for example, Al2O3. Known representative non-metallic inclusions of C type inclusions include, for example, oxide particles.
These non-metallic inclusions can be counted by microscopic observation in accordance with JIS G0555 “Microscopic testing method for the non-metallic inclusions in steel”. For example, the number of inclusions can be counted in the following manner. A specimen is cut off from a target, polished to be provided with mirror finish without etching, and observed with an optical microscope at 400×.
Next, with reference to
The count is then converted to the number per area of 1 mm2. The inclusions are counted on only one of the outer surface and the inner surface of each specimen. The number of the inclusions is divided by the area of the specimen, i.e., 2 mm×12 mm, whereby the number is converted to the number per area of 1 mm2. In the present embodiment, the inclusions appearing on the outer surface of each specimen was counted. Quantities of the inclusions were measured by the foregoing process.
The results shown in
Next, to study an effect exerted on the rolling fatigue characteristics by the residual ratio of the inside diameter-side thickness and that of the outside diameter-side thickness, test pieces having different residual ratios of the inside diameter-side and outside diameter-side thicknesses were prepared.
Rolling fatigue testers will be described with reference to
Tubular rotary components of Examples and Comparative Examples were produced to have different residual ratios of the inside diameter-side and outside diameter-side thicknesses. The produced tubular rotary components were subjected to heat treatment under the heat treatment conditions shown in Table 4 and a fine finishing process, whereby the following tubular rotary components were prepared: tubular rotary components of Examples 4-1 to 4-3 and Comparative Example 4 (having different residues ratio of the inside diameter-side thickness); and tubular rotary components of Examples 5-1 to 5-3, Comparative Examples 5-1 and 5-2 (having different residue ratios of the outside diameter-side thickness). The cutting process after the reaming-drawing process was performed so that a finishing allowance of 0.1 mm was left with respect to a desired shape. The fine finishing process after the heat treatment was performed to grind the tubular rotary component by about 0.1 mm, thereby achieving the desired shape.
The tubular rotary components of these Examples and Comparative Examples were subjected to rolling fatigue tests under the test conditions shown in Table 5. Table 6 shows a relationship between the residue ratio of the inside diameter-side thickness and the rolling fatigue characteristics. Table 7 shows a relationship between the residue ratio of the outside diameter-side thickness and the rolling fatigue characteristics. The tubular rotary components of Examples and Comparative Examples shown in Table 7 all have a height of 12 mm. The rolling fatigue test results are evaluated and indicated as follows.
Under the conditions shown in Table 5, a cumulative fracture probability of the tests in which n=16 was calculated. The tubular rotary component having the characteristics equivalent or superior to those of a tubular rotary component made of a seamless steel tube was evaluated as good, and is marked with circle symbol (o). The tubular rotary component having the characteristics inferior to those of the tubular rotary component made of a seamless steel tube was evaluated as poor, and is marked with cross symbol (x).
As shown in Table 6, in the cases of the tubular rotary components manufactured by the method including the cutting process step, if the residue ratio of the inside diameter-side thickness was equal to or greater than 0.37, good rolling fatigue characteristics were obtained. As shown in Table 7, if the residue ratio of the outside diameter-side thickness was equal to or greater than 0.49, good rolling fatigue characteristics were obtained.
Next, the following tubular rotary components were subjected to the rolling fatigue tests: the tubular rotary component of Example 4-1 (Table 6), the inside diameter side of which was subjected to the cutting process; the tubular rotary component of Example 5-1 (Table 7), the outside diameter side of which was subjected to the cutting process; and the tubular rotary component of Comparative Example 6 made from a seamless steel tube.
The tubular rotary component of Comparative Example 6 was made from a seamless tube of SUJ2 steel produced by the Mannesmann piercing method and having an outside diameter of 22 mm, an inside diameter of 10 mm, and a wall thickness of 6 mm. The seamless tube was subjected to a tube-drawing process to be formed into a shape with an outside diameter of 21.5 mm and an inside diameter of 9.8 mm. Subsequently, like Examples 4-1 and 5-1, the tubular rotary component of Comparative Example 6 underwent heat treatment and the finishing process to be formed into a shape with an outside diameter of 20 mm and an inside diameter of 12 mm. Thus, Comparative Example 6 has the residual ratio of the inside diameter-side thickness identical to that of Example 4-1, and the residual ratio of the outside diameter-side identical to that of Example 5-1.
The results of the rolling fatigue tests are illustrated in
The inner surfaces of the tubular rotary components of Examples 4-1 and 5-1 have better rolling fatigue characteristics than the inner surface of the seamless steel tube of Comparative Example 6. The outer surfaces of the tubular rotary components of Examples 4-1 and 5-1 have rolling fatigue characteristics equivalent to those of the outer surface of the seamless steel tube of Comparative Example 6.
Thus, in comparison with the case of producing a tubular rotary component from a seamless steel tube as a materiel, the manufacturing method of the present invention eliminates the need to cut off a considerable volume from the inner surface, improves material yield, and shortens time required for the cutting, thereby enabling an increase in productivity. Further, the manufacturing method of the present invention allows little difference in the rolling fatigue characteristics between the inner surface and the outer surface. Thus, the tubular rotary component of the present invention is suitable for inner and outer rings of a radial bearing.
In the foregoing, embodiments, modifications, and examples of the method for manufacturing the tubular rotary component according to the present invention have been described. However, the above-described embodiments, modifications, and examples are not intended to limit the present invention, and appropriate variations can be made to the present invention.
For example, in the above examples, the reaming-drawing process was performed once or twice. However, this is a non-limiting example. The reaming-drawing process may be performed more times, as necessary.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-014591 | Jan 2019 | JP | national |
This application is a Divisional Application of copending U.S. Application No. 17/426,912, filed Jul. 29, 2021, which is the National Phase under 35 U.S.C. § 371 of International Application No. PCT/JP2019/028297, filed Jul. 18, 2019, which claims the benefit under 35 U.S.C. § 119 (a) to Patent Application No. 2019-014591, filed in Japan on Jan. 30, 2019, all of which are hereby expressly incorporated by reference into the present application.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17426912 | Jul 2021 | US |
| Child | 18752897 | US |
